"But for red squirrels, stress brought on by social cues may be important to help offspring start off on the right foot."

I don't think this is quite right. I would say that the mother's stress is being used to help improve the ability of the offspring to survive in an environment with that level of stress.

It's not stated here, but growing faster than normal almost certainly is carrying some kind of cost. Might be an immune system cost, lifespan cost, etc. A reason why squirrels don't normally grow up at the accelerated rate.

So the response to stress is not helping the squirrels in absolute terms, it is helping them prepare for a particular set of environmental conditions. They would still probably be better off without the stress at all, allowing them to grow at a normal pace. But if the stress is present, then they may be better off growing fast to deal with it.

I suspect that this effect is more widespread than implied here, and growth and development is commonly affected by environmental factors. I wonder which of those factors is at play in human growth and development. What kinds of trade-offs do we make to deal with sub-optimal conditions?

Just about any sounds blasted by loudspeakers increase stress. I think the researchers are reaching when they ascribe specific reasons such as (faked) squirrel overpopulation to the stress the mothers experienced.

I cannot help but wonder if the process described in the article is less about the Mother Squirrel giving her offspring a chance and more about saving herself. Motherhood for those species that raise their young is a significant investment in time and energy. Perhaps she is working to get her progeny out of the house, so to speak, so that she may survive to breed again in less difficult circumstances.

Stress in rodents caused by auditory stimulation has previously been noted. I've cited this article before on Ars, but it bears repeating - Music can be hazardous to mouse health. (Warning: Probably not serious science)

Just about any sounds blasted by loudspeakers increase stress. I think the researchers are reaching when they ascribe specific reasons such as (faked) squirrel overpopulation to the stress the mothers experienced.

To clarify: the control squirrels also were exposed to playbacks, but rather than squirrel vocalizations, they heard bird calls.

Since female squirrels feed and care for their young, the researchers focused on how they responded to a booming squirrel population. They broadcast squirrel vocalizations over loudspeakers, signaling to wild squirrels that the environment was getting crowded.

Until I figured out the intended antecedant, I imagined the squirrel equivalent of an 80's era MC.

Stress is often considered to be a bad thing; we constantly hear about the health consequences of stress, and doctors often advise pregnant women to avoid stressful situations. But for red squirrels, stress brought on by social cues may be important to help offspring start off on the right foot.

This is presented as an apparent contradiction, but it's really not. Human health-and-wellness types care about lifespan and quality of life - the goal is to maximize the period of time that the organism is able to function independently and with sufficient capacity; it's a very complex topic, obviously. Evolution cares about EXACTLY one thing: how many offspring does the organism have, and how healthy are they (i.e. how likely are they to reproduce). From an evolutionary point of view, it's entirely reasonable to burn out the parental organism to maximize the offsprings' chances; and once the organism is past reproductive age, evolution cares not much about it's fate. Very, very different sets of priorities.